Question 40 1AE01 - First Assistant Engineer

The Correct Answer is A. ### 1. Why Option A (obstructed suction passage) is Correct: The rated fluid volume (flow rate) delivered by any positive displacement pump, including a radial piston hydraulic pump, is determined by the volume of fluid it can draw in (fill the pumping chambers) and subsequently expel. If the suction passage (inlet line or filter) is obstructed, the pump experiences cavitation or incomplete filling (starvation). This prevents the full volume of fluid from entering the piston chambers during the suction stroke, directly leading to a failure to deliver the full rated fluid volume, even if the pump mechanism itself is functioning correctly. ### 2. Why Other Options Are Incorrect: * **B) contaminated fluid:** While contaminated fluid can cause premature wear and lead to future flow degradation, the contamination itself does not immediately reduce the flow volume unless the particles are numerous enough to significantly increase viscosity (which is rare) or directly cause catastrophic wear. The immediate and primary effect of contaminated fluid is usually component damage (wear and scoring), not a direct loss of rated volume on its own. * **C) pitted thrust rings:** Thrust rings manage the axial forces and usually maintain the proper clearance between rotating components. Pitting would primarily cause excessive friction, heat, and potentially structural failure, but not necessarily a direct, immediate loss of volumetric efficiency (flow rate). Flow loss is typically caused by leakage paths, not friction components like thrust rings. * **D) worn pintle bearings:** Pintle bearings support the central shaft (pintle) of the pump. Wear in these bearings causes increased mechanical friction, vibration, and potentially misalignment, leading to pump seizure or mechanical failure. While mechanical failure eventually stops flow, the wear of the bearing itself does not directly create a leakage path that reduces the volume of fluid drawn in or pressurized. Volumetric efficiency loss is primarily tied to worn pistons, cylinder bores, or pintle *sealing surfaces*, not the support bearings.